is a test for contaminants in used lubricating oils,
under conditions prescribed by test method
ASTM-D-893. The oil is first diluted with pentane,
causing the oil to lose its solvency for certain oxidation
resins, and also causing the precipitation of such
extraneous materials as dirt, soot, and wear metals. These contaminants are
called pentane insolubles. The pentane insolubles may then be treated
with toluene, which dissolves the
oxidation resins (benzene was formerly used).
The remaining solids are called toluene insolubles. The difference in
weight between the pentane insolubles and the toluene insolubles is called
insoluble resins. Testing for grease insolubles is described in
ASTM-D-128.